Coffee has become one of the most popular beverages in modern society, with many different types and flavours of coffee being routinely available to a consumer, either in outlets such as coffee shops or in supermarkets for domestic use. The evolution of the popularity of coffee as a beverage has caused a shift in how coffee is being consumed, for instance in domestic settings.
Whereas in the past coffee would be predominantly brewed from instant coffee granules or from packaged ground coffee powders, e.g. using domestic coffee makers such as espresso machines or filter machines, nowadays a greater emphasis is placed on the freshness of the brewed coffee, which has triggered a rise in popularity of coffee roasting apparatuses. In such an apparatus, fresh, i.e. green, coffee beans can be roasted by a thermal process, e.g. using hot gases or by physical contact with a hot surface. During roasting at temperatures above 170° C., water is redistributed, and complex chemical reactions such as Maillard reaction and pyrolysis are induced. A fresh coffee powder can then be formed by grinding the freshly roasted coffee beans, thereby facilitating the brewing of fresh coffee. Such coffee is typically considered to have a superior taste compared to coffee brewed from packaged ground coffee powders.
The control of such a coffee roasting process is however far from trivial. Different users may require a different degree of roasting, e.g. a light roast or dark roast, of the coffee beans to cater for their personal taste. Moreover, different varieties of coffee beans will require different roasting times in order to achieve a certain roasting degree. Indeed, even different harvests of the same variety of coffee beans may exhibit variability in the required roasting times to achieve the desired degree of roasting. Therefore, one of the major challenges in providing a coffee roasting apparatus is to ensure that the roasted product meets customer expectation; e.g. has the desired degree of roasting.
Existing coffee roasting apparatuses such as the Nesco® Model CR-1000 Series of coffee roasters allow the user to specify the roasting time of the coffee beans in order to achieve the desired roasting result. Other roasting apparatuses offer control over the roasting process by allowing the user to specify the roasting temperature. However, as indicated above, it has been found that the desired roasting degree cannot be consistently achieved by (only) controlling the roasting time and/or temperature.